Size and volume of a shipment should be considered once loading the aircraft. Depends on the capacity a shipment may occupy in the holds of the aircraft or in ULDs, the freight charges can be increased.

As an example, an AKE (ULD) with dimensions of 156 x 153 x 160 CM have the capacity of almost 4CBM. This ULD is designed to carry around 700 to 800 KG of cargo. If the shipment is volumetric, the space occupied by that shipment should have the weight of about 700 KG. If the Gross Weight of that shipment is less than 700 KG, for example 400 KG, the customer has to pay the minimum weight of 700 KG for the space that his shipment has occupied.

Suppose that we have a shipment of cotton for 300 KG which occupies the whole space of one AKE. In this area that cotton occupied, carrier could be able to load around 700 KG, so Carrier will ask for payment of 700 KG freight charge to carry this load.

In AWB, there is a space to declare the Gross Weight (GW) of the shipment, and beside that, there is an space that shipper should declare the Chargeable weight (CHG WT).

It is easy to calculate the chargeable weight: Length X Width X Height in CMs divided by 6000. (L X W X H/6000). Some carriers or courier companies may use the figure of 5000. The biggest Length, biggest Width and biggest Height shall be considered.

However, there are times that a Carrier may ask for higher chargeable weight depends on the volume a shipment may occupy in ULD. For example, the maximum height of a PMC (ULD) is 160 CM. If a shipment has the height of 150 CM, it is almost impossible to find a cargo that can be loaded on top of this box, or may be the box cannot be stowed, as per shipper request, so customer has to pay for the maximum height. This will be considered in the length and width of a shipment comparing to the L & W of the ULD and whether there is sufficient space remained to load more cargo beside that special shipment.

This practice is used in other ways of transportation as well. If a truck is supposed to carry 20 TONS of cargo but a shipment of 12000 KG occupies the whole space, the customer has to pay for the full truck load price to the Carrier. Same goes on the vessel containers as well.

Normally in:

Sea Freight, 1CBM is considered to be 1000 KG

Land Transport, 1CBM is considered to have 333 KG cargo on it and,

Air Freight, 1CBM is considered to have 167 KG cargo on it.  

Chargeable Weight is the weight that shipper has to pay the freight charges based on that. It is called Volumetric Weight or Dimensional Weight as well. If the CHCBL WT is bigger than the gross weight, freight charges will be calculated based on CHGBL WT and if is lesser than Gross Weight, then the Gross Weight (GW) will be used in calculation of freight charges.  (More explanation: Ref.3.9 of IATA TACT RULES)